1. Field of the Invention
The present invention relates to an improved method for examining and modifying prototype circuit boards, and more specifically to the use of a light table for backlighting a circuit board of transparent dielectric material to permit viewing of the layered circuit traces on the circuit board.
2. Description of the Prior Art
The development of prototype circuit boards or "breadboards" has always been a time consuming and laborious process. Once a circuit concept has been schematically drawn, it is not in final form for a production-run circuit board. The arrangement of components and the circuit traces on the various layers or circuit planes of the circuit board still need to be laid out in an optimal manner to achieve the most efficient use of the circuit board geography, minimize possible interference among components and/or circuit traces on the circuit board, and to provide a circuit board layout which is logical and as easy as possible to follow should maintenance or modification be necessary. Thus, once a circuit schematic is prepared, there may be numerous board layout iterations before a final layout of the circuit board geography and its respective circuit planes is developed.
After the initial schematic is developed, the next usual step is to assemble a prototype circuit board in order to ascertain whether the circuit operates, to allow further testing and modification of the circuit itself, and ultimately to aid in laying out the circuit board geography and its circuit planes for circuit board production purposes. A prototype circuit board is often referred to as a "proto board," "brass board," or "wire wrap board." In each of these instances, a board medium is used which has embedded power and ground planes running therehrough, to allow components to simply be plugged in to the board and then wire wrap connected on the board (often using wire wrapping techniques). The final product in this case is a board with components populating one side and wires running to and fro on the other side. The advantage of this type of prototype circuit board is that the component mounting is temporary (not soldered) and modifications to the board can be made by rerouting the wires from component to component or to different component leads without scrapping the entire board. The boards used for such prototype arrangements are not printed circuit boards, except for the power and ground planes therein--all other circuitry is achieved by wire wrapping techniques.
In addition, because the power and ground planes are embedded in such prototype boards and the wire wrapping occurs typically on one side of the board, modification is sometimes difficult because the board must be turned over and back to ascertain what wire came from and went to a particular component or lead on a component. Tracing the circuit on a prototype wire wrap board is often difficult because the circuit schematic does not resemble the component layout on the board and if a component layout schematic has been developed, the necessity for looking at both sides of the board at the same time to determine where circuit traces start and end with respect to various components is difficult to do, laborious and easily subject to error.
For simple prototype circuits, wire wrapping boards are a quick and easy means for building a prototype circuit to allow testing and further modification. For more complex circuitry arrangements, however, a wire wrap board becomes quite complex and literally quite messy because of the wires running from component to component. In addition, because of the solderless connections and possible lengthy wires that might be needed between components, electrical performance of a prototype wire wrap board may be different from that intended by the design, or may differ from the final production board design (in final circuit board form, the components are typically arranged quite compactly with shorter circuit traces than in a prototype board for the same circuit). The need to be able to develop a prototype circuit board which is much closer to the final printed circuit board product has been long felt in the circuit board design industry.